Conformation of Cytochromes
V. CYTOCHROME c OXIDASE
Yash P. Myer 1
From the
1 From the Department of Chemistry, State University of New York at Albany, Albany, New York 12203
The conformation of cytochrome c oxidase at pH 7.4 has been examined by circular dichroism measurements in the Soret and the intrinsic absorption regions. The studies include the conformational characterization of native oxidized and reduced oxidase, and the corresponding complexes with cyanide and carbon monoxide, as well as investigation of the conformational effects associated with increasing concentrations of detergent, aging of the preparation, and the ionic nature of the detergent. It is concluded that the conformation of the prosthetic group is dependent upon the nature of the detergent used, the age of the preparation, and the valence state of heme a. The ionic detergent, deoxycholate, and aging alter the conformation of heme a, especially in the reduced state of iron, whereas oxidized oxidase seems to be more or less insensitive to both. In the ferric state of iron the purified preparation exhibits a complex Soret spectrum which is replaced by a single symmetrical peak upon reduction with dithionite. A conformational change from a rather asymmetric heme a environment to relatively symmetrical surroundings seems to accompany the valence change of iron. It is further concluded that there exists no heme-heme interaction in any of the valence states of the enzyme. In the intrinsic absorption region, the native enzyme and its complexes exhibit extrema at 222 and 210 nm, typical of proteins and polypeptides containing 
helical structures. The positive extremum, 197 nm, and the cross-over point, 204 nm, however, are indicative of the presence of other structures. The possibility of ß structure is considered.
Submitted on July 6, 1970
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